1. Field of the Invention
The present invention relates generally to a fly-back transformer, and is directed more particularly to a fly-back transformer with no case.
2. Description of the Prior Art
In the art, almost all fly-back transformers are constructed such that low voltage and high voltage windings are wound on the outer periphery of a core, the windings are housed in a case through which the core passes, and insulating material is introduced into the case to integrate the windings with the case. With the so-called prior art fly-back transformer with a case, the windings wound on the core are accommodated in the case as described above, so that the positioning of the windings relative to the case can be achieved correctly and there is no need to treat the end surface thereof by charging the insulating material into the case below its edge. However, since the prior aft fly-back transformer uses a case, it can not be made compact and its size becomes large. Further, upon manufacturing the prior art fly-back transformer, both the case making process and the charging process of the material, which covers the windings, into the case can not be carried out simultaneously and hence the working process requires many steps. Further, the covering of the windings requires two layers, which causes the construction to become complicated.
In the art, there has been proposed a fly-back transformer with no case which is free from the defects inherent to the fly-back transformer with a case. With the prior art fly-back transformer with no case, a low voltage winding and a high voltage winding are wound on a bobbin through which a core passes. The bobbin with both windings is loaded into a molding box, then molded by a resin, and thereafter, the core is inserted into the bobbin to be fixed thereto. Thus, the prior art fly-back transformer with no case is made. In this molding of the windings, however, when the windings are loaded into the molding box and then resin injected into the molding box, the coil bobbin is vibrated or swung by the injection pressure of resin. As a result, the winding bobbin becomes eccentric with respect to the molding box. If the molding of the winding bobbin is carried out with the above eccentric state, the products are poor in quality and hence low in yield. Further, with this molding, the resin material swells up along the peripheral surface of the molding box by a capillary phenomenon. This swelling causes the resin material to protrude from the molded surface as a burr after releasing. This burr causes trouble in treating, that is, attaching the winding bobbin to a machine chassis. Therefore, after molding, a surface treatment is necessary to remove the burr, which increases the manufacturing time.